| Under the situation that cultivated land resources are in shortage,increase crop yield per unit area by applying chemical fertilizer is an important way to alleviate the pressure of food demand and ensure food security.However,to achieve high crop yield,the excessive application of chemical fertilizer by farmers resulted in high input,low efficiency and high environmental costs.Therefore,it is of vital importance to explore the potential of sustaining crop yield,increasing nitrogen use efficiency and improving soil microbiological characteristics under optimized fertilization.Additionally,a trinity optimized fertilization management model of soil-microbe-crop should be constructed to achieve high yield,high efficiency and sustainablity of agriculture production.Combining farmer practices survey,meta-analysis and a-three-year field experiment,the present study comprehensively investigated the potential of nutrient regulation and its influence on crop productivity and soil fertility under the current situation facing severe challenges in agricultural production.At the same time,the response of soil microbial diversity to fertilization and its effect on agricultural ecology were explored by collecting soil samples under different fertilization regimes at the field experiment sites of rice-wheat rotation or maize-wheat/maize rotation system.The main findings obtained are as follows:1.The data of farmer practices survey showed that the averaged rice yield in Jiangsu province was 17%higher than that in China,while the nitrogen application rate in Jiangsu was 67%more than than that in China.This resulted in the lower PFPN in Jiangsu province,which was only 68%of that in China.Meta-analysis results showed that after reducing the N rate,the yield and PFPN increased by 2.8-5.7%and 52-77%,respectively,compared with traditional/conventional nitrogen application in Jiangsu province.The increased rice yield and PFPN were attributed to the regulated nitrogen uptake(-5.8--14%),which reducing the rice panicle number by 2.1-5.5%,while increasing the grains per panicle,seed setting rate and 1000-grain weight by 4.0-6.8%,2.0-3.9%and 0.9-2.1%,respectively.Moreover,the responses of rice yield formation and nitrogen uptake and utilization to the reducied nitrogen application was affected by rice varieties,reducing methods,reduction proportion,and basic soil fertility.The nitrogen reduction of rice in Jiangsu province can be realized by adjusting the nitrogen management and applying organic fertilizer,and the recommended reduction space is 31%,in which the basal and tillering fertilizer were the main decreasing direction.2.Compared with the farmer's nitrogen fertilization practices(NFPK),the yield of rice and wheat and the nitrogen fertilizer use efficiency were significantly increased by optimized fertilization practices(NOPK).The organic fertilizer substitute 20%nitrogen on the basis of the optimized fertilization practices(N80%OPKMI)could significantly improve the nitrogen fertilizer use efficiency on the premise of stable yield.The application of organic fertilizer is benefit for the high sustainability and stability of rice and wheat yield.Compared with Control treatment,the application of fertilizers,especially organic fertilizers,significantly increased the SOC and TN contents in soil.The contents of SOC and TN were significantly correlated with crop yields.3.In the rice-wheat rotation system,when compared with the chemically fertilized soil,the geometric mean of the assayed enzyme activities(GMea)in organically amended soils was significantly increased.In contrast,the microbial carbon-use efficiency:nitrogen-use efficiency ratio(mCUE:mNUE)was highest in chemically treated soil.These changes of microbial functional indicators were associated with the shifts in the bacterial and not the fungal community composition,despite the fact that both bacterial and fungal community compositions were significantly affected by the fertilization regimes.The abundances of specific soil bacterial taxa,especially the genera Luteimonas and Gemmatimona,were enriched by organic amendments.Soil organic carbon emerged as the major determinant of the bacterial community composition under short-term fertilization.4.In the rice-wheat rotation system,when compared with Control,short term application of chemical fertilizer significantly increased the abundance of bacterial amoA,narG,nosZ,and nifH genes.Compared with chemical-treated soil,the application of chemical fertilizer plus wheat straw increased the abundance of bacterial amoA,narG,nosZ,nifH and nirK genes.Compared with Control,the application of chemical fertilizer plus organic manure increased the abundance of all the nitrogen-cycling genes except archaeal amoA,nirS and napA genes.The change of bacterial amoA genes abundance contributed the most to the variations in the abundance of the nitrogen cycling community between different fertilization strategies.AOB contributed dominantly(82-85%)the nitrification in all of the fertilized soils.AOB amoA copy numbers(but not AOA)were significantly correlated with nitrification potential.Soil pH,SOC and NO3-were the most important factors influencing the abundance of microbial communities involved in the nitrogen cycle.5.In the maize-wheat/maize rotation system,long term fertilization resulted in significant changes in soil microbial communities and enzyme activities.The variation of enzyme activities in soil is significantly related to the variation of both bacterial and fungal community structures.Soil pH is the most important abiotic factor causing the changes of soil microbial communities and soil enzyme activities.The bacterial communities had more important roles than fungal communities in predicting the change of soil enzyme activities.6.In the maize-wheat/maize rotation system,after long term fertilization,the highest nitrification activity(44 mg N kg-1 soil d-1)was observed in only organic fertilizer treated soil,whereas the lowest activity(2.8 mg N kg-1 soil d-1)was observed in only mineral fertilizer treated soil.AOA dominated(94%)the nitrification in the Control soil,while AOB contributed dominantly(85-89%)in all of the organic amended soils,and chemical-treated soil showed an almost equal contribution to AOA(46%)and AOB(54%).Compared with the Control soil,AOA abundance increased in soils with organic and low chemical fertilizer but decreased in only chemically treated soil,whereas the AOB abundance in all fertilized soils was greatly enhanced.The AOA activity was linearly dependent on AOA abundance,whereas the AOB activity was exponentially correlated with AOB abundance.The sequences of AOA and AOB in the Control soil were mostly affiliated with group I.1b thaumarchaeota and genus Nitrosospira clusters 3a.1.Soil treated with chemical fertilizer increased the abundance of AOA that belonged to group I.la-associated lineage,whereas more abundant AOB was related to Nitrosospira clusters 3a.2 and 8b.In contrast,the organic-treated soil showed more abundant AOB that belonged to Nitrosospira clusters 3 b and 8b.The soil ammonium(NH4+)content was identified as the dominant driver of activity and diversity of AOA,and soil pH was considered to be the major influencing factor in abundance and composition of AOA;the AOB composition was mainly affected by soil NH4+content,the relative activity and diversity by soil pH,and the relative abundance by soil electrical conductivity.In summary,reasonable nitrogen fertilizer management and organic fertilizer application can reduce the amount of chemical nitrogen fertilizer on the premise of ensuring crop yield and improve the efficiency of crop nitrogen utilization.In addition,the application of organic fertilizer could improve the sustainability and stability of crop production.The application of organic fertilizer mainly improved the physical-chemical properties of soil,which in turn influenced the soil fertility by controlling the soil microbial community diversity,especially the bacterial community,promoting the expression of soil enzyme activity,and enhancing the functionality of microorganisms related to nitrogen cycle. |
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